1. Field of the Invention
The present invention relates to a three-phase brushless direct current (BLDC) motor system, and a circuit and method for driving a three-phase BLDC motor. More specifically, the present invention relates to a three-phase BLDC motor system, and a circuit and method for driving a three-phase BLDC motor using two Hall sensors.
2. Description of the Related Art
A general 3-phase brushless direct current (BLDC) motor includes a 3-phase (U-phase, V-phase, and W-phase) coil installed at a stator and a permanent magnet attached to a rotor.
A BLDC motor driving circuit provides current to the three phases of the coil installed at the stator of the 3-phase BLDC motor. The rotor of the motor is rotated according to a magnetic field generated by the current provided by the driving circuit. The rotor is continuously rotated in one direction by the sequential on and off switching of switching elements according to the position of the rotor. The switching elements detect the position of the rotor by detecting its magnetic field and change the direction of the current flowing through each phase of the stator coil based on the position of the rotor.
The position of the rotor is sensed by three Hall detectors, which sense the magnetic field of the rotor. These Hall sensors generate three signals, which have a phase difference of 120° between them. Hall detectors can be Hall sensors or Integrated Circuits (ICs).
FIG. 1 shows a conventional BLDC motor and a driving circuit. Conventional BLDC motor 10 includes a 3-phase (U phase, V phase, and W phase) coil 13 installed at a stator, a rotor 12 with a permanent magnet attached to it, and three Hall sensors 11a, 11b, and 11c that detect the intensity of a magnetic field of the rotor.
Hall sensor 11a senses the magnetic field of the rotor at its location and outputs two signals Hu+ and Hu− with a magnitude corresponding to the sensed magnetic field, which have a phase difference of 180°. Hall sensor 11b senses the magnetic field of the rotor at its location and outputs two signals Hv+ and Hv− with a magnitude corresponding to the sensed magnetic field, which have a phase difference of 180°. Hall sensor 11c senses the magnetic field of the rotor at its location and outputs two signals Hw+ and Hw− with a magnitude corresponding to the sensed magnetic field, which have a phase difference of 180°.
FIG. 2 illustrates the waveforms of the signals Hu+, Hu−, Hv+, Hv−, Hw+, and Hw−.
Referring to FIG. 1 again, motor driving circuit 40 receives the signals output from Hall sensors 11a-c and provides currents to 3-phase coil 13 to control the rotation of rotor 12. Motor driving circuit 40 has comparators 42a, 42b, and 42c. Comparator 42a receives the two signals Hu+ and Hu− output from Hall sensor 11a and outputs a Hall signal Hu. Comparator 42b receives the two signals Hv+ and Hv− output from Hall sensor 11b and outputs a Hall signal Hv. Comparator 42c receives the two signals Hw+ and Hw− output from Hall sensor 11c and outputs a Hall signal Hw. Hall signals Hu, Hv, and Hw are used for controlling a motor driver 44.
Motor driver 44 changes the direction of the currents flowing through the phases of the coil in response to the Hall signals, output from comparators 42a, 42b, and 41c. 
Conventional BLDC motor 10 and motor driving circuit 40 require three Hall sensors 11a, 11b, and 11c installed at the motor and six input terminals provided at the motor driving circuit 40, driving up the cost of the motor.